1. Field of the Invention
The present invention relates to a controller, and more particularly to a controller having an adjustable triangle-wave generator for modifying the amplitude and frequency of the triangle wave, changing the width and frequency of the controlled signal and enhancing the transient response of the loading system.
2. Description of the Related Art
Pulse width modulation (PWM) is a traditional controlling method applied to a system having the feedback circuit, such as the boosting circuit, the buck circuit, the push-pull circuit, half-bridge circuit or full-bridge circuit. In the prior art technology, a feedback voltage from feedback circuit is processed by the error amplifiers to generate a error signal, and then the error signal is compared with a fixed-amplitude triangle wave generated by a triangular-wave generator as to generate a pulse.
FIG. 5 is a block circuit diagram showing a conventional controller of a loading system. The loading system 50 comprises: a controller 500, a switch 550 and a loading circuit 560. The switch 550 is coupled to a power terminal, the controller 500 and a ground terminal. The input terminal 562 of the loading circuit 560 is coupled to the power terminal. The output terminal 564 of the loading circuit 560 is coupled to the ground terminal. The controller 500 is coupled to the output terminal 564 of the loading circuit 560.
The controller 500 comprises: a triangle-wave generator 510, an error amplifier 520, a comparator 530 and a driving circuit 540. A negative terminal of the error amplifier 520 is coupled to the output terminal 564 of the loading circuit 560 for receiving the feedback voltage therefrom. The positive terminal of the error amplifier 520 is coupled to a source of reference voltage. The positive terminal of the comparator 530 is coupled to the error amplifier 520, the negative terminal of the comparator 530 is coupled to the triangle-wave generator 510, and the output terminal of the comparator 530 is coupled to the driving circuit 540. FIG. 6 is a schematic drawing showing a conventional triangle-wave generator outputting the triangle wave, the error signal and the pulse controlling signal. The error amplifier 520 performs an error operation of the feedback voltage and the reference voltage for outputting an error signal 604 to the comparator 530. After the controller 500 is turned on, the triangle-wave generator 510 outputs a fixed-amplitude triangle wave 602 to the comparator 530. The comparator 530 compares the error signal 604 and the fixed-amplitude triangle wave 602 for outputting the driving signal. Finally, the driving circuit 540 outputs a pulse controlling signal 606 according to the driving signal.
In the loading system 50 in prior art, the switch 550 controls the power terminal to output electric power according to the pulse controlling signal from the comparator 530. When the switch 550 is turned on, the power is not transmitted to the loading circuit 560; if not, the power is transmitted to the loading circuit 560.
Accordingly, the conventional controller has the following disadvantages:
(1) In the conventional controller, because the width of the pulse controlling signal is modulated by the error of the feedback voltage and the reference voltage, noises in the feedback voltage will interfere with the width of the pulse controlling signal.
(2) The conventional controller with higher sensitivity generates a desired transient response for the loading system, but degrades the stability thereof.
(3) The conventional pulse modulator with lower sensitivity generates a desired stability of the loading system, but degrades the transient response thereof.